Method for producing coke, and coke

ABSTRACT

A method for producing a coke includes performing dry distillation of a mixture. The mixture includes: an ashless coal; an oxidized ashless coal obtained by an oxidation treatment of an ashless coal; and a raw petroleum coke. Relative to 100 parts by mass of a total of the ashless coal, the oxidized ashless coal and the raw petroleum coke, a content of the ashless coal is from 5 to 40 parts by mass, and a total content of the ashless coal and the oxidized ashless coal is from 30 to 70 parts by mass.

TECHNICAL FIELD

The present invention relates to a method for producing a coke, and a coke. More specifically, the present invention relates to a method for producing a coke suitable as a reducing material for non-ferrous metallurgy, and a coke.

BACKGROUND ART

Conventionally, a coke has been used as a reducing material in refining of a non-ferrous metal such as aluminum and titanium. In particular, a calcine coke (so-called calcined coke) obtained by heating a raw petroleum coke is inexpensive and therefore, is used for general purposes.

The raw petroleum coke as a raw material of the calcine coke is a by-product generated in the process of refining petroleum from crude oil. Accordingly, the character of the calcine coke is dependent on the crude oil. For example, the impurities (e.g., sulfur, nickel, vanadium, sodium and the like) contained in the calcine coke are derived from the crude oil as a raw material of the calcine coke. These impurities become a contamination source and therefore, in the case of using the calcine coke as a coke for use in refining, the content of the impurities (in particular, sulfur content; hereinafter the same) is required to be as small as possible. However, since the impurity content in the recently produced crude oil is large, it has been difficult to provide a coke with a small impurity content.

As regards a carbon material with a small impurity content, studies are being made to utilize, as the coke raw material, an ashless coal substantially containing no ash. For example, Patent Document 1 discloses a production method of an ashless coal to be used for a fuel, a coke raw material, a chemical raw material, etc.

However, the ashless coal has high thermal fluidity and has a property of melting at 200 to 300° C. irrespective of the grade of the raw material coal. In addition, the ashless coal has a property of expanding when it is heated at around 400° C. Therefore, when an ashless coal is subjected to forming, followed by dry distillation by high-temperature heating, the ashless coal melts, and the shape of the formed product cannot be maintained, leading to a problem with thermoplasticity. Furthermore, expandability is a problem, for example, as follows: the ashless coal may expand by undergoing foaming due to high-temperature heating to overflow from a dry distillation apparatus or adhere to the inner wall of the dry distillation apparatus, making its discharge impossible, or the coke may be obtained as a sponge-like porous body and extremely reduced in the bulk specific gravity. In this way, because of the problem with thermoplasticity or expandability, the ashless coke could be hardly used as a coke raw material.

To solve such a problem, the present inventors have proposed a technique for modification of the ashless coal (Patent Document 2). Specifically, a production method of a carbon raw material is disclosed, the method including a slurry heating step of heat-treating a slurry containing a coal and an aromatic solvent, a separation step of separating the slurry heat-treated in the slurry heating step into a liquid component having dissolved therein coal and a solid component composed of an ash and insoluble coal, an ashless coal obtaining step of obtaining an ashless coal by removing the aromatic solvent from the liquid component, and an ashless coal heating step of heat-treating the ashless coal obtained in the ashless coal obtaining step to provide a carbon raw material, wherein the volatile content of the carbon raw material obtained in the ashless coal heating step, as measured by the method specified in JIS M 8812, is less than 35 mass % and 24 mass % or more.

According to this technique, by virtue of including a slurry heating step, a separation step, an ashless coal obtaining step, and an ashless coal heating step for adjusting the volatile content to fall in a predetermined range, a low-ash carbon material having excellent self-sinterability can be produced.

PRIOR ART LITERATURE Patent Documents

Patent Document 1: JP-A-2001-26791

Patent Document 2: JP-A-2009-144130

SUMMARY OF THE INVENTION Problems that the Invention is to Solve

The technique of Patent Document 2 produces an excellent effect in improving self-sinterability, but since modification of the ashless coal requires a lot of labor, the productivity is not necessarily high, and the modified ashless coal is relatively expensive.

The present invention has been made by focusing on the above-described circumstances, and an object of the present invention is to provide a method for producing a high-purity coke at a lower cost than ever before, and to provide a high-purity coke.

Means for Solving the Problems

The method for producing a coke in the present invention which is capable of achieving the object includes performing dry distillation of a mixture containing: an ashless coal; an oxidized ashless coal obtained by an oxidation treatment of an ashless coal; and a raw petroleum coke, in which, relative to 100 parts by mass of a total of the ashless coal, the oxidized ashless coal and the raw petroleum coke, a content of the ashless coal is from 5 to 40 parts by mass, and a total content of the ashless coal and the oxidized ashless coal is from 30 to 70 parts by mass.

Preferable embodiments of the present invention include the case where the mixture is subjected to forming, and then, the dry distillation is performed, the case where a percentage of increase in oxygen of the oxidized ashless coal is from 2 to 10%, the case where the oxidation treatment is an air oxidation, and the case where the oxidation treatment is performed at a temperature of 150° C. or more and less than an ignition point.

In addition, the preferable embodiments include the case where the dry distillation is performed in a chamber furnace, and the case where the dry distillation is performed in a rotary kiln.

An aspect of the present invention includes a coke produced by performing dry distillation of a mixture, the mixture containing: an ashless coal; an oxidized ashless coal obtained by an oxidation treatment of an ashless coal; and a raw petroleum coke, in which, relative to 100 parts by mass of a total of the ashless coal, the oxidized ashless coal and the raw petroleum coke, a content of the ashless coal is from 5 to 40 parts by mass, and a total content of the ashless coal and the oxidized ashless coal is from 30 to 70 parts by mass.

Advantage of the Invention

According to the production method in the present invention, a high-purity coke can be produced at a low cost by using a raw petroleum coke. In addition, in the present invention, a high-purity coke can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart for explaining one example of the production process of an ashless coal.

FIG. 2 is a flowchart for explaining one example of the production process of a coke in the present invention.

MODE FOR CARRYING OUT THE INVENTION

The present inventors have made many intensive studies to provide a high-purity coke at a low cost by using a raw petroleum coke as a carbon raw material, and found the followings.

The impurity content of the ashless coal is very small, and mixing of the ashless coal with the raw petroleum coke is useful for reducing the impurity content of the coke. However, as pointed out in conventional techniques, an ashless coal has a problem with thermoplasticity or expandability.

Studies of the present inventors revealed that when the ashless coal is subjected to an oxidation treatment, the thermoplasticity and expandability of the ashless coal can be improved. However, the oxidized ashless coal is in the form of fine powder and exhibits low caking, and dry distillation of a mixture of the oxidized ashless coal and the raw petroleum coke causes a problem that the coke obtained becomes powdery and readily scatters out of a dry distillation apparatus and in addition, the bulk specific gravity of the coke is reduced. Intensive studies have been made to solve such a problem, and as a result, it has been found that when a mixture of an ashless coal, an oxidized ashless coal and a raw petroleum is made, the ashless coal functions as a binder for binding the oxidized ashless coal and the raw petroleum coke and a problem such as powdering of the coke can be suppressed.

It has been then found that when a mixture containing the ashless coal, the oxidized ashless coal and the raw petroleum coke each with a predetermined content described later is used, the coke obtained can be prevented from melting or expanding and a high-purity coke could be provided at a low cost.

The coke production method in the present invention is described below by referring to the flowcharts illustrated in FIGS. 1 and 2.

First, the ashless coal used in the present invention is described.

An ashless coal indicates a coal having an ash content of 5 mass % or less, preferably 3 mass % or less. The ashless coal is preferably a coal in which the ash concentration of a residual inorganic material (e.g., silicic acid, alumina, iron oxide, lime, magnesia, alkali metal or the like) when heated at 815° C. to thereby form an ashed body thereof is very low. Specifically, the ash concentration is more preferably 5,000 ppm or less (on the mass basis), still more preferably 2,000 ppm or less. In addition, the ashless coal is absolutely water-free and exhibits higher thermal fluidity than the raw material coal.

<Production Process of Ashless Coal>

The ashless coal can be obtained by various conventional production methods and, for example, may be obtained by removing a solvent from a solvent extract of a coal. For example, the ashless coal can be obtained through the following steps S1 to S3 (see, FIG. 1), but the ashless coal production process (S1 to S3) described below may be appropriately changed, and various treatment steps may be added, if desired.

For example, in the production of an ashless coal, as long as each of the above-described steps is not adversely affected, other steps, e.g., a coal pulverization step of pulverizing the raw material coal, a removal step of removing an unwanted material such as refuse, or a drying step of drying the obtained ashless coal, may be provided between respective steps above or before or after each step.

<Slurry Heating Step: S1>

The slurry heating step (S1) is a treatment of mixing a coal and an aromatic solvent to prepare a slurry and heat-treating the slurry to extract a coal component in the aromatic solvent.

The kind of the coal as a raw material (hereinafter, sometimes referred to as “raw material coal”) is not particularly limited. For example, various known coals such as bituminous coal, subbituminous coal, brown coal and lignite can be used. In view of profitability, it is more preferable to use a low-rank coal such as subbituminous coal, brown coal and lignite, instead of using an expensive high-grade coal such as bituminous coal.

The aromatic solvent is not particularly limited as long as it is a solvent having a property of dissolving a coal. Examples of the aromatic solvent include a monocyclic aromatic compound such as benzene, toluene and xylene, and a bicyclic aromatic compound such as naphthalene, methylnaphthalene, dimethylnaphthalene and trimethylnaphthalene. In addition, examples of the bicyclic aromatic compound include aliphatic side chain-containing naphthalenes, biphenyl, and a long-chain aliphatic side chain-containing alkylbenzene. In the present invention, a bicyclic aromatic compound that is a non-hydrogen-donating solvent, is preferred.

The non-hydrogen-donating solvent is a coal derivative that is a solvent primarily purified from a carbonization product of a coal and mainly composed of a bicyclic aromatic compound. The reason why a non-hydrogen-donating solvent is preferred is that the non-hydrogen-donating solvent is stable even in a heated state and excellent in the affinity for a coal and therefore, the ratio of a coal component in the solvent (hereinafter, sometimes referred to as “extraction percentage”) is high and in addition, because the solvent can be easily recovered by distillation or other methods and furthermore, the solvent recovered can be cyclically used.

If the boiling point of the aromatic solvent is too low, the pressure required during heating extraction or in the later-described separation step (S2) would be high, and the loss due to volatilization in the step of recovering the aromatic solvent is increased, leading to a decrease in the recovery ratio of the aromatic solvent. Furthermore, a decrease in the extraction percentage during heating extraction is caused. On the other hand, if the boiling point of the aromatic solvent is too high, separation of the aromatic solvent from a liquid component or a solid component in the separation step (S2) is difficult, and the recovery ratio of the solvent lowers. The boiling point of the aromatic solvent is preferably from 180 to 330° C.

The coal concentration relative to the aromatic solvent is not particularly limited. Although it may vary depending on the kind of the raw material coal, if the coal concentration relative to the aromatic solvent is low, the ratio of the coal component extracted in the aromatic solvent to the amount of the aromatic solvent would be small, and this is not profitable. On the other hand, a higher coal concentration is better, but if the coal concentration is excessively high, the slurry viscosity would be increased, and transfer of the slurry or separation between a liquid component and a solid component in the separation step (S2) is likely to become difficult. The coal concentration, on the dry coal basis, is preferably 10 mass % or more, more preferably 20 mass % or more and preferably 50 mass % or less, more preferably 35 mass % or less.

If the heat treatment (heating extraction) temperature of the slurry is too low, the bonding between molecules constituting the coal cannot be sufficiently weakened, and in the case of using a low-rank coal as the raw material coal, the resolidification temperature of the ashless coal obtained in the later-described ashless coal obtaining step (S3) cannot be elevated. On the other hand, if the heat treatment temperature is too high, the pyrolytic reaction of the coal would be very active to cause recombination of pyrolytic radicals produced, leading to a decrease in the extraction rate. The slurry heating temperature is preferably 350° C. or more, more preferably 380° C. or more, and preferably 420° C. or less.

The heating time (extraction time) is not particularly limited, but if the extraction time is long, the pyrolysis reaction proceeds excessively, allowing for the progress of a radical polymerization reaction, and the extraction ratio lowers. For example, at the above heating temperature, the heating time is preferably 120 minutes or less, more preferably 60 minutes or less, still more preferably 30 minutes or less, and preferably 10 minutes or more.

After the heating extraction, the extract is preferably cooled to 370° C. or less so as to suppress a pyrolysis reaction. The lower limit of the temperature when cooling is preferably 300° C. or more. If cooled to less than 300° C., the dissolving power of the aromatic solvent is reduced, and reprecipitation of the once extracted coal component occurs, leading to a decrease in the yield of ashless coal.

The heating extraction is preferably performed in a non-oxidizing atmosphere. Specifically, the heating extraction is preferably performed in the presence of an inert gas such as nitrogen. This is because contact with oxygen during heating extraction is risky due to a fear of ignition and when hydrogen is used, the cost rises.

The pressure in the heating extraction may vary depending on the temperature during heating extraction or the vapor pressure of the aromatic solvent to be used, but if the pressure is lower than the vapor pressure of the aromatic solvent, the aromatic solvent is vaporized and not confined in a liquid phase, and extraction cannot be achieved. On the other hand, if the pressure is too high, the equipment cost and operation cost are increased, and this is not profitable. The preferable pressure is generally from 1.0 to 2.0 MPa.

<Separation Step: S2>

The separation step (S2) is a step of separating the slurry heat-treated in the slurry heating step (S1) into a liquid component and a solid component. The liquid component is a solution containing the coal component extracted in the aromatic solvent. The solid component is a slurry containing an ash insoluble in the aromatic solvent and an insoluble coal.

The method for separating the slurry into a liquid component and a solid component in the separation step (S2) is not particularly limited, and a conventional separation method such as filtration method, centrifugal separation method and gravity settling method, may be employed. In the present invention, it is preferable to use a gravity settling method enabling continuous operation of a fluid and being low-costly and suitable for treatment of a large amount. In the case of employing a gravity settling method, a liquid component (hereinafter, sometimes referred to as “supernatant liquid”) that is a solution containing a coal component extracted in the aromatic solvent can be obtained from the upper part of a gravity settling tank, and a solid component (hereinafter, sometimes referred to as “solid content concentrate”) that is a slurry containing a solvent-insoluble ash and a coal can be obtained from the lower part of the gravity settling tank.

Subsequently, as described below, the aromatic solvent is separated and recovered from the supernatant liquid by using a distillation method, etc., and as a result, ashless coal having a very low ash concentration can be obtained (ashless coal obtaining step (S3)).

<Ashless Coal Obtaining Step: S3>

The ashless coal obtaining step (S3) is a step of separating the aromatic solvent from the supernatant liquid to obtain an ashless coal having a very low ash concentration.

The method for separating the aromatic solvent from the supernatant liquid is not particularly limited, and a general distillation method, evaporation method (e.g., spray drying method), etc. can be used. The aromatic solvent recovered by separation can be repeatedly used. By the separation and recovery of the aromatic solvent, the ashless coal can be obtained from the supernatant liquid. The obtained ashless coal can be used as a raw material of the mixture in the present invention, and also can be used as a raw material of the oxidized ashless coal.

<Other Steps>

If desired, a byproduct coal in which the ash is concentrated may be produced by separating the aromatic solvent from the solid content concentrate (byproduct coal obtaining step). As the method for separating the aromatic solvent from the solid content concentrate, a general distillation or evaporation method can be used, similarly to the above-described ashless coal obtaining step (S3) of obtaining an ashless coal from a liquid component.

<Production Process of Coke>

The production method of the coke in the present invention is described below by referring to FIG. 2. In the production of the coke, as long as each step is not adversely affected, other steps, e.g., a pulverization step of pulverizing various raw materials, etc., a removal step of removing an unwanted material such as refuse, or a step of applying various treatments to the obtained coke, may be provided between respective steps or before or after each step.

<Oxidation Step: C1>

The oxidation step is a step of applying an oxidation treatment to the ashless coal to obtain an oxidized ashless coal. By applying an oxidation treatment to the ashless coal, the ashless coal is modified, and the thermoplasticity or expandability can be improved.

The method for oxidizing an ashless coal is not particularly limited. It is desirable to perform oxidation in an oxidizing atmosphere such as oxygen, ozone, nitrogen dioxide and air, and air oxidation using oxygen in air as an oxidizer is preferred.

The percentage of increase in oxygen of the oxidized ashless coal is not particularly limited, but if the percentage of increase in oxygen is too low, the modification effect on the ashless coal is not sufficient, and a problem attributable to thermoplasticity or expandability is sometimes caused during the dry distillation. On the other hand, if the percentage of increase in oxygen is too high, the yield is reduced, and as a result, this is not profitable. Accordingly, the percentage of increase in oxygen is 2% or more, preferably 3% or more, and is preferably 10% or less, more preferably 5% or less.

In the present invention, when the percentage of increase in oxygen of the ashless coal is set, an ashless coal having a lower percentage of increase in oxygen than the set value is not dealt with as the oxidized ashless coal in the present invention even if the ashless coal has been subjected to an oxidation treatment. In addition, in the case where an ashless coal having a lower percentage of increase in oxygen than the set value is used as a carbon raw material, the ashless coal is dealt with as the ashless coal in the present invention,

The percentage of increase in oxygen as used in the present invention is a value obtained by measuring the oxygen content percentage of an ashless coal before and after oxidation treatment according to JIS M8813 (Calculation Method of Oxygen Percentage) and making calculation (oxygen content percentage of oxidized ashless coal—oxygen content percentage of ashless coal).

The temperature kept during oxidation (hereinafter, oxidation temperature) may be appropriately adjusted so that the desired percentage of increase in oxygen can be obtained. If the oxidation temperature is low, the ashless coal may be insufficiently oxidized, and the above-described modification effect may not be fully exerted. In addition, if the oxidation temperature is low, a long time is required to achieve the desired percentage of increase in oxygen, and the productivity is reduced. On the other hand, if the oxygen temperature is too high, the oxidation rate is excessively increased, and the oxidation degree of the ashless coal can be hardly controlled. The oxidation temperature is preferably 150° C. or more, more preferably 200° C. or more, and is preferably less than the ignition point of the ashless coal, more preferably 350° C. or less.

The oxidation time (holding time at a predetermined temperature) may be appropriately adjusted so that the desired percentage of increase in oxygen can be obtained. If the oxidation time is short, the ashless coal may be insufficiently oxidized. On the other hand, if the oxidation time is long, the ashless coal may be excessively oxidized, and the yield is reduced to cause an increase in the cost. For example, the oxidation time in the above-described temperature range is preferably 0.5 hours or more, more preferably 1 hour or more, and is preferably 6 hours or less, more preferably 3 hours or less. After the oxidation, the ashless coal may be allowed to cool to room temperature.

The particle diameter (equivalent-circle diameter; hereinafter, the same applies to the particle diameter) of the ashless coal subjected to an oxidation treatment is not particularly limited. If the particle diameter of the ashless coal is too large, the inside of the ashless coal may not be sufficiently oxidized, leaving a fear of occurrence of melting, etc. during the dry distillation. On the other hand, if the particle diameter of the ashless coal is too small, the handling property is deteriorated. The average particle diameter of the ashless coal is preferably 3 mm or less, more preferably 1 mm or less, and is preferably 0.2 mm or more, more preferably 0.3 mm or more. From the standpoint of accelerating the oxidation, the maximum particle diameter is also preferably 3 mm or less, more preferably 1 mm or less, still more preferably 0.5 mm or less.

<Carbon Raw Material Mixing Step: C2>

The carbon raw material mixing step is a step of mixing the ashless coal, the oxidized ashless coal, and a raw petroleum coke, thereby obtaining a mixture (hereinafter, referred to as “mixed carbon raw material”).

The raw petroleum coke is a solid substance by-produced, in the petroleum refining process, together with light oil in equipment (coker) for producing light oil by heating a distillation residue at a high temperature (for example, at 500° C. or more) to cause pyrolysis. In the present invention, as for the raw petroleum coke, various known raw petroleum cokes available on the market can be used. A raw petroleum coke having a volatile content of 5 to 20 mass % and a sulfur content of 2 to 5 mass % is preferred.

In the present invention, the mixing ratio of the ashless coal in the mixed carbon raw material and the mixing ratio between the ashless coal and the oxidized ashless coal must be appropriately controlled according to the properties of the ashless coal (oxidized/non-oxidized, oxidation degree) so as to produce a high-purity coke.

(I) Content of Ashless Coal: From 5 to 40 Parts by Mass

If the mixing ratio of the ashless coal is too small, the function as a binder is not sufficiently exerted, and the coke becomes powdery. On the other hand, if the mixing ratio of the ashless coal is too large, thermoplasticization or expansion due to the ashless coal becomes excessive and, for example, the coke may be obtained as a sponge-like porous body and reduced in the bulk specific gravity, or the coke may adhere to the inner wall of a dry distillation apparatus, making its discharge impossible.

In the present invention, the content of the ashless coal is 5 parts by mass or more, preferably 10 parts by mass or more, and is 40 parts by mass or less, preferably 25 parts by mass or less, per 100 parts by mass of the total of the ashless coal, the oxidized ashless coal, and the raw petroleum coke.

(II) Total Content of Ashless Coal and Oxidized Ashless Coal: From 30 to 70 Parts by Mass

As described above, the total content of the ashless coal is 40 parts by mass or less, but by containing the oxidized ashless coal, the amount of the raw petroleum coke used can be more decreased, and the impurity content in the coke can be more reduced. The ashless coal and oxidized ashless coal are more expensive than the raw petroleum coke and therefore, when the total content of those is increased, the unit cost of the coke rises. On the other hand, if the total content of the ashless coal and oxidized ashless coal is too low, the effect of reducing impurities is not sufficiently obtained. For this reason, the total content of the ashless coal and oxidized ashless coal is 30 parts by mass or more, preferably 35 parts by mass or more, more preferably 40 parts by mass or more, and is 70 parts by mass or less, preferably 65 parts by mass or less, more preferably 60 parts by mass or less, per 100 parts by mass of the total of the ashless coal, the oxidized ashless coal and the raw petroleum coke.

The content of the oxidized ashless coal is not particularly limited, but if the content of the oxidized ashless coal is too small, there is caused a problem that, for example, the coke expands to have a sponge-like structure or melts and sticks in an apparatus. Therefore, the content of the oxidized ashless coal is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, still more preferably 30 parts by mass or more, per 100 parts by mass of the total of the ashless coal, the oxidized ashless coal and the raw petroleum coke. On the other hand, the upper limit of the content of the oxidized ashless coal may be appropriately adjusted to fall in the above-described range of the total content of the ashless coal and the oxidized ashless coal (from 30 to 70 parts by mass) but it is preferably 50 parts by mass or less, more preferably 40 parts by mass or less.

The average particle diameter of the ashless coal is not particularly limited, but if the average particle diameter of the ashless coal is too large, a non-uniformity may be produced in the mixed state of the mixture, not allowing the ashless coal to fully exert a binder effect, etc. On the other hand, if the average particle diameter is too small, the handling property may be deteriorated. The average particle diameter of the ashless coal is preferably 10 mm or less, more preferably 0.5 mm or less, and is preferably 0.1 mm or more, more preferably 0.2 mm or more. If the maximum particle diameter of the ashless coal is too large, a non-uniformity may be produced in the mixed state in a formed product, and for this reason, it is preferably 1.0 mm or less, more preferably 0.5 mm or less.

In addition, the average particle diameter of the ashless coal is preferably smaller than the average particle diameter of the oxidized ashless coal, because a gap between carbon raw materials is filled and the binder effect is more enhanced.

The mixture in the present invention may be sufficient if it contains the ashless coal, the oxidized ashless coal, and the raw petroleum coke, and the mixture may contain other material(s) (for example, a known additive such as a binder and a petroleum pitch) as long as the present invention is not adversely affected, but in the case of containing other material(s) in the mixture, the impurity content of the coke may be increased due to the other material(s). Therefore, the total of the ashless coal, the oxidized ashless coal and the raw petroleum coke in the mixture is preferably 90 mass % or more, more preferably 100 mass %. The 100 mass % indicates that the mixture consists of the ashless coal, the oxidized coal and the raw petroleum coke and the remainder is impurities.

The method for mixing the ashless coal, the oxidized ashless coal and the raw petroleum coke is not particularly limited, and a conventional method ensuring uniform mixing may be employed. Examples thereof include a mixer, a kneader, a single-shaft mixer, and a double-screw mixer.

<Forming Step: C3>

The forming step is a step of forming, if desired, the mixture obtained in the carbon raw material mixing step (C2) into a desired shape to obtain a formed product. By making a formed product from the mixture, binding between respective carbon raw materials can be more firmly created due to the binder effect of the ashless coal, and powdering of the coke or reduction in the bulk specific gravity can be suppressed.

For example, in the case of dry distillation of the mixture in a chamber furnace, a load applies in the vertical direction, reducing the distance between respective carbon raw materials, and respective carbon materials are bound by the binder effect of the ashless coal, so that the coke can be prevented from powdering and the bulk specific gravity can be increased. Such an effect can be more enhanced by making a formed product.

On the other hand, in the case of dry distillation of the mixture by use of a horizontal furnace in which a sufficient load does not apply in the vertical direction, such as rotary kiln, the binder effect is not fully exerted. As a result, binding between respective carbon raw materials is weak, and the coke is likely to be powdered, leading to a reduction in the bulk specific gravity of the coke. Therefore, the mixture is preferably formed into a desired shape before the dry distillation.

The method for making a formed product from the mixture is not particularly limited and examples thereof include, for example, a method using a double roll (twin roll)-type forming machine by means of flat rolls or a double roll-type forming machine having an almond-shaped pocket, a method using a single-shaft press-type forming machine or roller-type forming machine or an extrusion forming machine, and press forming by means of a mold, and any of these methods can be employed. Among them, it is preferable to make a briquette-like formed product or sheet-like formed product by means of a double roll-type briquetter, roll compaction, etc.

Forming of the mixture may be cold forming that is performed at around room temperature, but hot forming performed under heating is preferred. When the mixture is formed under pressure at a high temperature, the ashless coal is plastically deformed to fill voids between the oxidized ashless coal particles and the raw petroleum cokes, so that a more highly densified formed product can be obtained. In turn, a coke having a higher bulk specific gravity can be obtained by dry distillation of the highly densified formed product. On the other hand, if the forming temperature is too high, the ashless coal may be softened and expanded, failing in achieving a high bulk specific gravity. The hot forming temperature (the temperature of a device such as mold or roll) is preferably 100° C. or more, more preferably 200° C. or more, and is preferably 450° C. or less, more preferably 300° C. or less. The forming pressure is not particularly limited, and conventional conditions may be employed. For example, the forming pressure is approximately from 0.5 to 3 ton/cm².

<Dry Distillation Step: C4>

The dry distillation step is a step of performing dry distillation of the mixture obtained in the carbon raw material mixing step (C2) or the formed product obtained in the forming step (C3), thereby acquiring a coke. The shape of the furnace used for dry distillation is not particularly limited, and dry distillation may be performed batchwise by using a chamber furnace or dry distillation may be performed continuously by using a vertical shaft furnace. In addition, a horizontal rotary furnace such as rotary kiln may also be used.

As for the dry distillation conditions, conventional conditions may also be employed, and the dry distillation temperature may be appropriately set and is not particularly limited but may be preferably 650° C. or more, more preferably 700° C. or more, and preferably 1,200° C. or less, more preferably 1,050° C. or less. The dry distillation time at the dry distillation temperature is not particularly limited as well, and a desired dry distillation time may be set according to the apparatus configuration, etc. and may be preferably 5 minutes or more, more preferably 10 minutes or more, and preferably 24 hours or less, more preferably 12 hours or less.

The dry distillation atmosphere may be a non-oxidizing gas atmosphere so as to prevent deterioration of the coke due to oxidation. As the non-oxidizing gas, various known gases may be used, and the gas may be, for example, an inert gas such as nitrogen, helium and argon, or a reducing gas such as hydrogen gas.

During dry distillation, not only the raw petroleum coke is converted to calcine coke (calcined coke) but also the ashless coal acts as a binder between the oxidized ashless coal and the calcine coke to firmly bond the oxidized ashless coal to the calcine coke, thereby enhancing the coke strength.

In the case of subjecting the mixture to dry distillation, respective carbon raw materials are bound to each other, and amorphous agglomerate-shaped coke is obtained. In addition, when the mixture is formed, the coke having substantially the same shape as that of the formed product before dry distillation is obtained. In the coke in the present invention, the blending ratio of the ashless coal is appropriately controlled, so that the coke can be kept from adhering to the inside of the dry distillation apparatus, which makes its discharge impossible, and also from powdering.

The thus-obtained coke has higher purity and higher bulk specific gravity than those of conventionally known coke. Specifically, the content of minerals that become impurities is preferably 1 mass % or less, more preferably 0.5 mass % or less. The bulk specific gravity is preferably 0.53 g/cm³ or more, more preferably 0.6 g/cm³ or more, still more preferably 0.7 g/cm³ or more, and most preferably 0.8 g/cm³ or more. The sulfur content is preferably 2 mass % or less.

In addition, the mixture is free from the above-described problem attributable to thermoplasticity or expandability during the dry distillation and in turn, the coke obtained is excellent in the appearance and can be discharged from the dry distillation apparatus.

As described above, the coke produced by performing dry distillation of a mixture containing the ashless coal, the oxidized ashless coal obtained by an oxidation treatment of an ashless coal, and the raw petroleum coke, in which, relative to 100 parts by mass of the total of the ashless coal, the oxidized ashless coal and the raw petroleum coke, the content of the ashless coal is from 5 to 40 parts by mass and the total content of the ashless coal and the oxidized ashless coal is from 30 to 70 parts by mass, is a coke having a high purity and a high bulk density and succeeded in improving the above-described thermoplasticity and expandability which may emerge as a problem in the case of using an ashless coal.

EXAMPLES

The present invention is described more specifically below by referring to Examples, but the present invention is, of course, not limited to the following Examples and may be carried out by appropriately making changes as long as they are in conformity to the gist described hereinabove and hereinafter, all of which are included in the technical scope of the present invention.

(Production of Ashless Coal) (Slurry Heating Step: S1)

With 5 kg of the raw material coal (bituminous coal), an aromatic solvent (1-methylnaphthalene (produced by Nippon Steel Chemical Co., Ltd.)) in an amount (20 kg) four times that of the raw material coal was mixed to prepare a slurry. This slurry was pressurized with nitrogen of 1.2 MPa and subjected to a heat treatment (heating extraction) in an autoclave having an internal volume of 30 liter under the conditions of 370° C. and 1 hour.

(Separation Step: S2)

The obtained slurry was separated into a supernatant liquid and a solid content concentrate in a gravity settling tank maintained at the same temperature and pressure.

(Ashless Coal Obtaining Step: S3)

The obtained supernatant liquid was further filtered (stainless mesh filter with an opening size of 1 μm) to obtain an ashless coal solution. The aromatic solvent was separated and recovered from the ashless coal solution by a distillation method to produce an ashless coal. The obtained ashless coal was pulverized so as to pass through a sieve having an opening size of 3 mm, whereby the ashless coal was obtained.

(Measurement of Sulfur Content)

This ashless coal was measured for the sulfur concentration by the method specified in JIS M 8122. As a result, the sulfur content of the ashless coal was 0.5 mass %.

(Production of Coke) (Oxidation Step: C1)

A part of the ashless coal was pulverized so as to pass through a sieve having an opening size of 0.5 mm. The pulverized ashless coal was heated in an air atmosphere to a predetermined temperature shown in Table 1 and held at the same temperature for a predetermined time, thereby performing an oxidation treatment (in Table 1, “Oxidation Conditions”). After the oxidation treatment, the ashless coal was allowed to cool to room temperature, whereby an oxidized ashless coal was obtained.

Here, the ashless coal and the oxidized ashless coal were measured for the oxygen concentration before and after the oxidation treatment, according to JIS M 8813, and the percentage of increase in oxygen of the oxidized ashless coal was calculated. The results are shown in Table 1 (in Table 1, “Percentage of Increase in Oxygen”).

(Raw Petroleum Coke)

Commercially available raw petroleum coke (volatile content: 9.5 mass %, sulfur content: 3.1 mass %) was pulverized so as to pass through a sieve having an opening size of 10 mm.

(Carbon Raw Material Mixing Step: C2)

Ashless coal (“A” in the Table), oxidized ashless coal (“B” in the Table), and raw petroleum coke (“C” in the Table) were mixed in a predetermined ratio shown in Table 1 (in Table 1, “Blending Ratio of Raw Materials”) to obtain a mixture.

Here, in No. 16, the ashless coal subjected to the oxidation treatment was dealt with as an ashless coal, because the percentage of increase in oxygen was less than 2% (1.50%). Accordingly, although the blending ratio of No. 16 was A:B:C=50 (20 mass % of ashless coal not subjected to an oxidation treatment+30 mass % of ashless coal having a percentage of increase in oxygen of 1.5%):0:50, in order to show details of the blending ratio of No. 16, for convenience sake, the blending ratio (“20”) of the ashless coal not subjected to an oxidation treatment is shown in column A of the Table, and the blending ratio (“30”) of ashless coal having a percentage of increase in oxygen of 1.5% despite having been subjected to an oxidation treatment is shown in column B.

(Forming Step: C3)

With respect to a part of the mixtures (Nos. 7 to 12 and 15; in the Table, “Presence or Absence of Forming”=done), a formed product was produced under the following conditions:

Forming method: roll compaction method

Roll temperature: 100° C.

Roll diameter: 162 mm

Roll width: 60 mm (pyramid-shaped groove)

Inter-roll width: 2 mm

Roll rotational speed: 15 rpm

Linear pressure: 3 ton/cm

(Dry Distillation Step: C4)

The mixture (Nos. 1 to 6, 13, 14 and 16 to 25) and the formed product (Nos. 7 to 12 and 15) were subjected to a dry distillation treatment in a chamber furnace (Nos. 1 to 6 and 15 to 25) or in a kiln (Nos. 7 to 14).

(Dry Distillation Treatment in Chamber Furnace)

The mixture (Nos. 1 to 6 and 16 to 25) or the formed product (No. 15) was added into a graphite crucible having an inner volume of 1,000 mL to provide a bulk specific gravity of 0.85 g/cm³, followed by heating to 1,000° C. at a rate of 3° C./min in a nitrogen atmosphere, and held at the same temperature for 5 hours to perform dry distillation, thereby producing a coke.

(Dry Distillation Treatment in Rotary Kiln)

The mixture (Nos. 13 and 14) or the formed product (Nos. 7 to 12) was inserted into a heated rotary kiln (diameter: 200 mm, total length: 4,000 mm) at an insertion rate of 1 kg/l. As for the heating temperature of the rotary kiln, the temperature was adjusted to an inlet temperature of 400° C. and an outlet temperature of 1,000° C. It was held at the temperature above for 60 minutes in a nitrogen atmosphere to perform dry distillation, thereby producing a coke.

(Evaluation Method)

The obtained coke was measured for bulk specific gravity, sulfur content, appearance, and presence or absence of adhering to the inside of the apparatus.

(Bulk Specific Gravity) (in the Table, “Bulk Specific Gravity after Dry Distillation (g/cm³)”)

A wooden cubic container whose one side is 100 mm was filled with the coke, and the bulk specific gravity was determined from the dry mass (W: g) of the coke which had been filled with the container. In this Example, the coke was judged to be passed when the bulk specific gravity was 0.53 g/cm³ or more.

(Sulfur Content) (in the Table, “Sulfur Content after Dry Distillation (%)”)

The sulfur concentration of the coke was measured in the same manner as for the ashless coal. In this Example, the coke was judged to be passed when the sulfur content was 2.0% or less.

(Appearance, Presence or Absence of Adhering to Inside of Apparatus) (in the Table, “Coke Characteristics”)

The appearance of the coke was observed with an eye and evaluated. In the case of performing dry distillation treatment in a chamber furnace (Nos. 1 to 6 and 15 to 25): the coke that was agglomerate-shaped was judged as “Excellent” (in the Table, “PE”); the coke that was agglomerate-shaped but slightly expanded (the bulk specific gravity: 0.53 g/cm³ or more and less than 0.7 g/cm³) was judged as “Pass” (in the Table, “P”); the coke that was powdery was judged as “Fail” (in the Table, “F”); and the coke that adhered and could not be discharged (in the Table, “FA”) or that expanded (in the Table, “FB”), was also judged as “Fail”. The appearance is ranked in the order of PE>P>(F, FA, FB).

In the case of performing dry distillation treatment in a kiln (Nos. 7 to 14): the coke that was flaky and free from occurrence of expansion, cracking, chipping or powdering was judged as “Pass” (in the Table, “P”); the coke that was powdery or experienced expansion, cracking, chipping or powdering was judged as “Fail” (in the Table, “F”); and the coke that adhered and could not be discharged was also judged as “Fail” (in the Table, “FA”). The appearance is ranked in the order of P>(F, FA).

TABLE 1 Percentage of Blending Ratio of Presence or Bulk Specific Sulfur Content Oxidation Increase in Raw Materials, Absence of Dry Distillation Gravity After Dry After Dry Coke No. Conditions Oxygen A/B/C (mass %) A + B Forming Method Distillation (g/cm³) Distillation (%) Characteristics 1 200° C., 1h   3%  4/48/48 52 none chamber furnace 0.45 1.6 F 2 200° C., 1h   3%  5/47/48 52 none chamber furnace 0.75 1.7 PE 3 200° C., 1h   3% 10/40/50 50 none chamber furnace 0.72 1.7 PE 4 200° C., 1h   3% 20/30/50 53 none chamber furnace 0.79 1.7 PE 5 200° C., 1h   3% 40/10/50 53 none chamber furnace 0.63 1.7 P 6 200° C., 1h   3% 42/10/48 52 none chamber furnace 0.49 1.5 FB 7 200° C., 1h   3%  4/48/48 52 done kiln 0.39 1.6 F 8 200° C., 1h   3%  5/47/48 52 done kiln 0.58 1.6 P 9 200° C., 1h   3% 10/40/50 50 done kiln 0.74 1.7 P 10 200° C., 1h   3% 20/30/50 50 done kiln 0.81 1.6 P 11 200° C., 1h   3% 40/10/50 53 done kiln 0.53 1.6 P 12 200° C., 1h   3% 42/10/48 52 done kiln — 1.5 FA 13 200° C., 1h   3% 10/40/50 50 none kiln 0.40 1.7 F 14 200° C., 1h   3% 20/30/50 53 none kiln — 1.6 FA 15 200° C., 1h   3% 20/30/50 50 done chamber furnace 0.81 1.6 PE 16 200° C., 0.3h 1.50% 20/30*/50 50 none chamber furnace 0.52 1.7 FB 17 200° C., 0.5h   2% 20/30/50 53 none chamber furnace 0.67 1.7 P 18 300° C., 0.5h   6% 20/30/50 50 none chamber furnace 0.77 1.6 PE 19 300° C., 1h   10% 20/30/50 50 none chamber furnace 0.72 1.5 PE 20 200° C., 1h   3% 20/20/60 40 none chamber furnace 0.79 1.8 PE 21 200° C., 1h   3% 20/10/70 30 none chamber furnace 0.82 1.9 PE 22 200° C., 1h   3% 20/5/75 25 none chamber furnace 0.81 2.1 PE 23 200° C., 1h   3% 20/40/40 60 none chamber furnace 0.89 1.3 PE 24 200° C., 1h   3% 20/50/30 70 none chamber furnace 0.92 1.1 PE 25 200° C., 1h   3% 20/60/20 80 none chamber furnace 0.91 0.8 PE

As shown in Table 1, in Nos. 2 to 5, 8 to 11, 15, 17 to 21, 23 and 24 satisfying the predetermined requirements of the present invention, the coke was of high purity with a sulfur content of 2.0% or less, and the bulk specific gravity thereof was also high. In addition, expansion, etc. during the dry distillation treatment were sufficiently suppressed, and the coke characteristics were good. Here, in No. 5 where the blending ratio of the ashless coal was high, the coke slightly expanded. In No. 17 where the percentage of increase in oxygen was lower than other cases, modification of the oxidized ashless coal was inferior to other cases, and the coke slightly expanded.

No. 1 is the case where the blending ratio of the ashless coal was low. In this case, since the content of the ashless coal functioning as a binder was small, the coke was powdered by the dry distillation treatment.

No. 6 is the case where the blending ratio of the ashless coal was high. In this case, since the content of the ashless coal was large, expansion occurred during the dry distillation treatment to not only yield sponge-like (porous) coke but also greatly reduce the bulk specific gravity.

No. 7 is the case where the blending ratio of the ashless coal was low. In this case, since the content of the ashless coal was small, powdering occurred in the kiln during the dry distillation treatment.

No. 12 is the case where the blending ratio of the ashless coal was high. In this case, not only the ashless coal was melted during the dry distillation but also the formed product was foamed and expanded, and as a result, the coke adhered to the inner wall of the kiln and could not be discharged.

No. 13 is the case where the mixture was not subjected to forming and the powder was directly subjected to dry distillation in the kiln. In this case, since an adequate pressure was not applied to the mixture during the dry distillation, the oxidized ashless coal and the raw petroleum coke could not be sufficiently bound and the coke remained in a powder form.

No. 14 is the case where the mixture was not subjected to forming and the powder was directly subjected to dry distillation in the kiln. In this case, the oxidized ashless coal and the raw petroleum coke could not be sufficiently bound, similarly to the case of No. 13, and since the ashless coal content was increased and larger than the case of No. 13, the coke adhered to the inner wall of the kiln due to melted and expanded ashless coal and could not be discharged.

No. 16 is the case where the oxidation time was short relative to the oxidation temperature and in turn, the percentage of increase in oxygen was low. In this case, since the content of the ashless coal (the total of the ashless coal and the ashless coal which had been subjected to an oxidation treatment but having a percentage of increase in oxygen of less than 2.0%) was too large without containing the oxidized ashless coal in which the percentage of increase in oxygen of the ashless coal is 2.0% or more, the ashless coal was foamed and expanded during the dry distillation treatment, and the bulk specific gravity was reduced.

No. 22 is the case where the blending ratio of the raw petroleum coke was large. In this case, the sulfur content after dry distillation was large, and the purity of the coke was low.

No. 25 (Reference Example) is the case where the blending ratio of the raw petroleum coke was small. In this case, the coke having a small sulfur content and a high bulk specific gravity was obtained, but since the blending ratio of the raw petroleum coke was small, the coke was expensive.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention.

This application is based on Japanese Patent Application No. 2013-251219 filed on Dec. 4, 2013, the contents of which are incorporated herein by way of reference.

INDUSTRIAL APPLICABILITY

In the present invention, the coke suitable, e.g., as a reducing material for non-ferrous metallurgy can be produced at a low cost. 

1. A method for producing a coke, comprising performing dry distillation of a mixture containing: an ashless coal; an oxidized ashless coal obtained by an oxidation treatment of an ashless coal; and a raw petroleum coke, wherein, relative to 100 parts by mass of a total of the ashless coal, the oxidized ashless coal and the raw petroleum coke, a content of the ashless coal is from 5 to 40 parts by mass, and a total content of the ashless coal and the oxidized ashless coal is from 30 to 70 parts by mass.
 2. The method for producing a coke according to claim 1, wherein the mixture is subjected to forming, and then, the dry distillation is performed.
 3. The method for producing a coke according to claim 1, wherein a percentage of increase in oxygen of the oxidized ashless coal is from 2 to 10%.
 4. The method for producing a coke according to claim 1, wherein the oxidation treatment is an air oxidation.
 5. The method for producing a coke according to claim 1, wherein the oxidation treatment is performed at a temperature of 150° C. or more and less than an ignition point.
 6. The method for producing a coke according to claim 1, wherein the dry distillation is performed in a chamber furnace.
 7. The method for producing a coke according to claim 2, wherein the dry distillation is performed in a rotary kiln.
 8. A coke produced by performing dry distillation of a mixture, the mixture containing: an ashless coal; an oxidized ashless coal obtained by an oxidation treatment of an ashless coal; and a raw petroleum coke, wherein, relative to 100 parts by mass of a total of the ashless coal, the oxidized ashless coal and the raw petroleum coke, a content of the ashless coal is from 5 to 40 parts by mass, and a total content of the ashless coal and the oxidized ashless coal is from 30 to 70 parts by mass. 